Automatic telephone system



2 Sheets-Sheet l TTL-lllh-{lls. L EL W. T. POWELL AUTOMATIC TELEPHONE SYSTEM Filed Dec.

ATTORNEY March 24, 1931.

w. T. POWELL 1,797,926

AUTOMATIC TELEPHONE SYS-TEM Filed Dec. l0. 1928 2 Sheets-Sheet 2 Marh 24, ll93l.

MOPUUZ ZOU ATTORNEY Patented Mar. 24, 1931 wiNrREn fr. PowELL, oF Aitcomis'riii-3,?`

cAnLsoN TELEPHONE MANUFACrU coaronArioN or Niiw Yom:

NEW, Your; rissIGNon'To 'riin sriaoMBERG- iNcooMrnNY, or RocHnsfrEaNEw YoRiQ-A AUTOMAT TELEHO'NE SYSTEM ,i

Application filed December 1 0, 1928. Serial No. 324,930.

This invention relates to telephone systems and more particularly to telephonesyfstems in which automatic switches are' directively operated by impulses. A g g a A 5 In former automatic telephone systems much difliculty has'been-encountered in obtaining uniform transmission of yimpulsesr over long or short subscribers"telephonelines Where the telephone lineor impulse circuits. or subscribers loop is long or has high resistance the impulses become greatly attenu-V ated whereas with short telephone lines or subscribers7 loops impulses are only slightly attenuated and are therefore strong'.l Theim# an impulse relay'must therefore be designed to respond to such weak and strong im.

, that a calling subscriber whose telephone line pulses which necessitates wide marginal lim` its ofthe impulse relay or impulse receiving equipment.V a very careful adjustment of the impulse relay but also constant attention so that the impulse relay will operate an automatic switch or switches reliably on signals these two extreme conditions.

Even with this care it is necessary to employ 'additional re i peating equipment or relaying' devices to ,fby emolng telephonefele from its take care of extremely long telephone lines to which the impulse relay cannot be satisfactorily adjusted;

strong signals transmitted over the short lines in the use of electrical means which compfensates for variations inthe signals by aug'nient- Y 9' the signals an amount inversely proporrelay or other impulse receiving equipment.

connection sol that if the calling subscriber immediately initiates a second call, this primar 1 trunk is available for use, y Y

For a clearer understanding of the'invention reference is made tothe drawings-.in which that portion of Fig. l at the'le'ft of the broken line represents pulse receiving or repeating equipment such Y This condition not only requires received under are not strengthened. Theinvention consists -net 7, its armature and back phone line and its associated line switch while at the lright Vof thebrokeii line of Fig. l there is represented a selector switch having incorporated therein circuits of the present invention. At the'rightand above the broken line f Fig. 2 there is represented a repeater incorporating the features of the present invention while below. kthebrolren line4 thereis represented a connector leading to a called subscribers line. y y

I The line switches7 selectors and connectors referred to in this disclosure are 'of the type now well known in the art.,

It is'believedthat'the invention will best be .understood by tracingthe operations that Y ytake place in establishing different types of telephone connections. Let it be assumed is represented at A desires to establish a telephone connection to a called subscriber whose telephone line indicated at B terminates in the same office as the calling line so that in the case of this call, conditions are such that it is not necessary to employ an arrangement now known in the art as a repeater.

-When the subscriber at A initiates a call switchhook the slow releasing line relay 5 is operated over the two sides ofthe subscribers `telephone line or loopl inV series, In accordance with the present invention itH-thrOugll the armatures and back contacts of is proposed to compensate or strengthen weak f signals to a predetermined strength whereas fout-off relay. With the line relay 5 operated, the ,motor magnet 7 which progressivelyadvances'thebrushes 8, 12 and 13 of vthe line fswitch, is actuated-in a circuit eX- tending from grounded battery throughV its winding, yarmature and ture `and .front contact of relay 5, test brush back Contact, arma-r eok 8y of theline switch to ground, over the test terminal such as 9 of' a busy trunlr, which Ground is applied to this test terminal, over b A further feature of the invention relates to a delayed release of the primary trunk of al ,Y

conductor 81, Yleftfliand armature and front contact `of the slow. releasing-relay 80, individual to the busy trunk. A circuit in Vmultiple of that justrdescribed extends from grounded battery,winding of the motor magcontact, winding of the cut-off relay 6, outer front contact and armature of the linefrelay 5 to ground.

a subscribers telerlhis last described circuit is ineffective to vopi272 i Y erate the cut-oil1 relay 6 at this time since this contact of relay 11 to the cathode. The conrelay is shunted by the ground connection astrol electrode is connected to an adjustsociated with the test terminals of busy trunks able Contact of rheostat 16. It Will be recalled as long' as the line switch is testing such terthat the' impulse circuit extending to the minals. Let it be assumed thatthe first 'idle v"right'handwindings of relay 15 includes the trunk encountered is that shown at the right resistancelunit 16, and incase of this long in F ig. 1, Which idle condition i-s-indieated--line-the current flow therethrough is at- `by the absence of :ground potential on its tenuated. vThe currentlowing through the VtestY terminal v9.V Underthis condition .the 'Ires'istance` 16 isfsuliciently lov so that the ymotor magnet no longer has `its Aope'rz'tt'ing N}'A `Otential"drop across -it is Vnot sufficient to circuit completed and consequently does not bias the control electrode of the vacuum tube advance the line switch brushes/8,. 12.and-:13-Hto prevent current flowing in its anode circuit and the short circuit about the cut-olf relay which it will be remembered includes the left 6 is no longer e'lectivesov this-relay isener- Tlhand Winding-of' relay 15. Therefore this ized in the circuit previously described. anode current develops a flux of the same V'hen Voperated relay 6 closes Ya locking cir# *polarity as'tlie other two windings as indimagnet'?, i*catedbythearrows. .Consequently the imllower frontvcontact" and arma--ipulseis-reenforcedforcompensated so that the '^*ture, test'brush18,5testfterminalf9andthence impulse relay 15 is effectivelyv operated in re- 'to ground at the innerfright'lia'nd arma/ture -fsponse tofeachi-mpulse.

L Let lit .now 1 lbe assumed that the :sub-

f The current cl'oeesiits-upper "fioWsL-finfthe impulse circuit through the rearmaturesfan'd ifrontfcon'tacts to extend-the -fsis'tance 16 and the right hand windings of 5 rheo'stat' lt'an'dl right'hfandfwindingof relay trol' element of the vacuum tube. 15 to grounded battery. lThis circuitope'rates duces the current flow in the anode circuit inthe rel ay 15l and thereby vcompletes actuatin,f g=circuit for 'slow'relfeasing'relay 11 from subscribers telephone line throughf the line relayliandwillbe correspondingly greater @switch brushes 12,'fand 13,g through the up- `perarinatu'res and'back contacts of relay 14,

'than inthe case'of-the long subscribers line and consequently there Willfbe a larger drop through the middle Windingvof'relay 1'5 to vin :potential across the resistance 16, thereby ground and through theresistan'ce element offproducing a more negative bias on the con- This recluding the left hand'winding of relay 15 and 1 the magnetizing force of its armature is 'f' grounded battery through itsWinding. front thereby -reduced to a predetermined amount.

contact of "relay 15, lowerrnost contacthand v "armature of=relay`14;toground. It-Will be seen that thevacuum' :tube 17 with its asso- "noted that the'iiiipulse relay 15has its Wind Ciated circuits operates as a self-regulator or :ings 'so arranged as'indicatedbylar'rowslthat :compensatorwforthe adjustment of the imthe fluir developed by each isetecti've inthe l'pulserelay -15 causing this Yrelay to attract its same direction. 1 s 1 "armatureWith-uniform ypull in spite of the The operations just disclosedwhich take fact'vthat-it is connected to telephone lines of 'place 'in' the course of the selection of an idle 1 fdiderent constants or. characteristics.

trunk 'are eXecutedfinf' a very short timeso AWith the relay 15' eneroized in the manner thatwhen the subscriber at"`substati`onf-A-ac-clescribed, a slow releasing relay 11 is op- I readiness to receive the rst series of impulses. "lowermost tuates the impulse device-associated vtheremuni `attenuation of the signal so that a small current Aflowsl through the'res'lsta'nce unit and the gh-t hand lWith the selector circu'itsof F 1 `are 2in 5 front Contact fand' armature of relay 15,

A Contact and armature of relay 14 It'will first be assumed thatthe A'subscribes ftOfgrOHnd- The relay 1l when operated line A is a longline with the' resultingmaxi`M Causes relay y80 to apply a busyvpotential and L16 this trunk as previously mentioned. Relay windings Of'rela'y 15,A TheA 1-11 at its le'fthand armature and front contact relay 15 is adjusted tocperate.properlykvithff'closes a breakpoint inthe operating circuit this current ilow'when re'enfo'rcedby'f the curi ofthe primary motor magnetl of the selector "rent flow through its` left hand'windingfas SWCL y wllbe described. It'wll beaotedthatavaev When the 'Subscrberat substation A opcharge device is associated fwith thesele'c'tor 'the first 'digit 0f the Called subscribersilill, Circuit, This device has a :Cahodef lgfenep the impulse relay 15' responds to ea ch of these gized from any Suitable Source: as fran; 19v impulses and ateach retraction of its arma-v y andis also providedWith a control' electrode WTC: Completes' an Operating CA'cut for the 2O and an anode`21. The' anode "21, isffc'on- "primary 'motor magnet 23 of Ethe selector nected in series'with the left'hand Wii'idingcausing` this-:magnet tof elevate Vthe selector offra-ay 157 B vbftm-QQ ndthenbethrough *brushesfj24,f25, 4an'dfQG one step in their prithe outermost righthand armature and frbnt mary-dir'ection. This'` operating circuit is ZFrom the foregoing description it will bev erated from grounded battery, its Winding,`

aholdingground to the ltest terminal 9 of' llO lSO

traced'irom grounded-battery, winding of the motor magnet 23, winding of the slow releasing change-over relay 27, front contact and armature or relay 11, back contact and armature of relay 15, lower back Contact and armature of relay 14 toground. As is well known the slow releasing change-over relay 27' is energized on'the iirst retraction of the armature of the impulse relay 15 and remains energized until the close of lthis series oi impulses. The Aprimary motor magnet is operated in this circuit each time that the impulse relay responds to an impulse from the impulse sender. At the close of the series of impulses the relay 15 holds its armature retracted for a relatively long interval which causes the deenergization of the slow releasingrelay 27. As soon as the selector switch has made one step in its primary movement the primary ott normal sets of contacts 28 and 29 are closed and as soon as the changeover relay 27 is energized, the relay 30 has 'its operating circuit completed from grounded battery, winding or this relay, back conj tact and armature of the secondary motor magnet 31 and primary oi normal contacts 28, inner front contact and armature of relay 27, inner armature and 'front contact of relay 11 to ground'. As soon as the relay 30 is energized it closes fa locking circuit Vfor itself through 'ts lower front contact and armature, which circuit is independent of the control or change-over relay 27 The operation of the relay 30 also closes a brealr point in the driving circuit of the secondary motor magnet 31but this circuit is ineffective until the change-over relay 27 deenergizes at the close of the firstseries of impulses at which time the secondary motor magnet begins to advance the selector brushes 24, and 26 in their secondary movement, The driving circuit of the secondary motor magnet is `closed from grounded battery, wind-V ing of this magnet, upper armature and contact of relay 30, armature and back contact of relay 27, front contact land armature or relay 11 tofground. 'Vhen thev secondary -motor magnet is energized in this manner, it

opens the locking circuit-or the relay and ladvancesfth'e selector brushes into engagement with rthefirst trunk of the selected group. If this trunk is busy,- its test terminal corresponding to-test terminal 32 is characterized by the lpresence of ground potential so that the relay 30v is now operated from grounded battery, winding of this relay, back contact and* armature of secondary motor magnet 31, contacts 28, conductor 33,

'back contact and armature of relay 14,7conductor 34, 'test brush 26 and. thence to ground over the test termin al of the busy trunk. r1`he operation of the relay 30 again closes the 'driving circuittorv the motor magnet 31 whereupon yit advances the selector brushes into engagementr with a second vtrunk and 36, winding of change opens theoperating circuit of relay 30 and the motor magnet 31 continues until -the test brush' 26' encounters the test terminal of an ofrelay 11. Relay 14 whenoperated at its Yupper armature and back contacts disconnects the impulse relay 15 of the iirs't selector from the calling subscribers line and eX- tends this lineV through' its upper armatures `and iront contacts to Vground and grounded battery through the right hand windings of the impulse relay 35 of the connector switch.

Also when relay 14 isoperated itcloses a locking circuit for itself throughV its inner' lower front contact and armature, holding conductor 34, test brush 26, test terminal 32 of the selected trunk to ground at the front contact and armature of the slow releasing relay 3G which attracts its armature as soon as the impulse relay 35 is operated. Relay 80 is now held over conductors 10 and 34.

The connectorswitch is now in readiness i to receive the tens series of impulses from the impulse sender atthe calling substation. The vacuum tube or electron discharge de` vice 37l with the left hand winding onf the impulse relay 35, Jfunctions in the same manner as the corresponding equipment at the selector switch and compensates or reenforces weak signals. In response to each of the tens series of impulses, the impulse relay 35 retracts its armature and thereby closes a circuit `from ground, its armature and back contact, armature and front contact of relay of primary motor magnet 39, side switch wiper 40 in its first position,lto grounded battery. The change-over relay is energized on the first completion rof this circuit and remains energized during this series-of im# pulsesr vwhile primary motor magnet 39 in Vresponse to each completion of this circuit advances the connector brushes 42, 43 and44 one step in their primary direction. At the close of the seriesA or tens impulses the impulse relay 35 holds its armature attracted, causing the change-over relay 38, which has been holding the escape magnet 45 operated, The escape magnet 45 then deenergizes and moves the side switch wipers into their second position. The rconnector circuits are now in readiness to receive the units series of impulses and in response to each impulse a circuit is closed from ground,

-over relay 38, winding armature andbacl contact of impulse relay A armature andbacltcontact `of test. relay 40, windingof the secondary motor magnet 4l, side switch wiper in its second position lto grounded battery. -The change-over relay 38 is energized on the tirstfimpulseor1 this series and remains energized until the close of this series of-impulses In response toeach of these units impulses the secondary motor magnet 41 advancesthe brushes 42, 43, and 44 one step in their secondary movement. At the close of these series of impulses the called line is tested.

-In the event that theca'lled line is busy, its ktest terminal 47 will be characterized by a. ground potential so that the escape magnet willbe held operatedV even when the relay 38 deenergizes atthe close of:` the series of impulses. vThis holding circuitfor the escape magnet is `closed. from grounded battery, re-

sistance unit, winding of escape magnet 45,`

continuity spring andv back Contact of relay 38,winding oftestA relay 40, its continuity spring; and back contact, side switch wiper 48 ina its second-position, test brush 44 and test terminal 47.: to ground. The test relay v40 is operated in Lits circuit and completes a locking circuit for` itself and the escape-niagnetV through: its continuity spring and otinormal contactsV 48,- to ground. lVith'the test relayr40zoperated'a .source of busy tone current BZ'is connected through its left hand contactlandl armature to the trunlrwhich terminates in: this connector switch from which trunk 4it is transmitted over the portion of theconnection al-ready established to the calling substation where .the calling subscriber hears the'busyv signal and releases the connection in a manner'to be described.

-Letit be assumed that the called line is idle when itis tested at the; close Aoi" the -units seriesof impulses, under. which assumption, there is an absence of ground potential on its test terminal 47 which prevents the test relay 40 from energizing and causes theescapemagnet to deenergize and move= the side switch wipers into their third position where `inging current is applied to the called line. This ringing current is supplied through the trip relay 50 andthe side switch wipers 51 and 52 and thence to the ringer at the called substation over the subscribers loop. Also as soon as the side switch wipers move to their third position escape-magnet 45 is operated in a circuit completed through the side switch wiper Vihen the called subscriber at B answers, the trip relay 50 is energizedandat its varmature and contact closes a circuit which short circuits, the esca-pe-magnet'45 causing it to deenergize and thereby move the side switch lwipers to their talking position. v'lallring current is supplied to= the calling: subscriber-eline through .the right hand windings of the impulse relay 35, while talking current is supplied to the called subscriber through the windings of the im- -pedance coil .54. Y

At the close of the conversation when the calling subscriber at station A replaces the receiver ,on its switchhook, the impulse relay 35 deenergizes and the slow releasing relay 36 deenergizes .which is ellective to close an operating circuit for the release magnet 55 from grounded battery, its winding, ofi-normal Vcontacts 56, back contacts'and armatures oi' of this holding circuit releases the relay 14,A

which has been holding the selector, to oper` ate the Areleasemagnet 58 from grounded battery, winding of the release magnet, oil-normal contacts 29, back Contact. and armatures of relays ll, l5, and -14 for releasing the selector. The slow releasing relay held operated over conductor 34 inmultiple with relay. 14 releases much-more slowly than relay 14 so that the holding `control of. the conductor 8l is maintained for a substantial interval after. the release of the connector. rIhis feature lmownas .delayed disconnect or the primary trunk will be more fully described hereinafter.

The present invention may be used with a repeater such asis shown above the dotted line in Fig. 2v which repeater i-s employed in connection with the repeating orrelaying of impulses. over a long trunk to an incoming second selector located at a distant oliiee. In the casey of a call to such an oliice, the line switch and selector of. Fig. l are operated in the manner previously described except that the selector is advanced to select an idle repeater such as shown in Fig.2.

As soonas this repeater is seized bythe lrstselector the calling subscribers line is extended through thebrushesrl2 and 13 of the line switch and the selectorv brushes 24 and 25 to the conductors `5.() and 60 of the trunk and thence through the two lower windings of the impulse relay 61, conductor 59 leading through theupper continuity spring and back contact of relay 62,- through the "resistance unit 63 andy middle winding of' relay 61 to grounded battery, while trunk conductor 60 is extended through the lower continuity spring and back contact of re1ay62 and lower winding of relay 6l toeground. The impulse relay 6l is energizedover this circuit and the slow releasing relay Y64 has its energizing circuit completed from grounded' battery, its windarmature of Ireing, inner front contactand lay 61 toy ground, thereby causing `this relay irom the ycalling been connected to a long teleplioneline there will be a relatively small drop in potential cross the resistance unit. 63 so that the control eleinent of the vacuum tube or electrode discharge device 67fis ai'lected insuch away that current in the anode circuit` including the upper winding/ofl the relay '.61 supplements the effectA of current over the impulse circuit and thereby `compensates for Vthe ,weak impulse current. Y n I unit 63 will be large sothat the control electrode oftliefvacuumtube v67 will be biased in sucha way that the anode current ywillbe relatively small and therefore eiiect'a v'uniformattraction of/thearmature of impulse relay 6l under allconditions.l f In response to the impulses from theimpulse transmitter subscriberls substation the impulse. relay 6l vibrates kits lowermost armature to cause intermittent makes and breaks -o ing the relay 8,0 may in the impulse repeating circuitto'tlie incoining second selector which circuitincludes Acon- Y ductor 68, upper armaturevand'front Contact of relay 65, lowermost viront contact and armature of relay 6l and conductor691 It is believedunnecessary to-.disclose the circuits of the incoming second selectorV or the iinal connector switcliinto which it oper- 62, upper, backrocontact and armature tof relay o .lay @siemens armatures to reverse ,theconnections ofthe ates, since theyy aresubstantially similar to the first selector shownin-Fig. 1 and the conf nector shownin theelowerpartI of Fig.. It is suiiicient to `,state rhowever vthat vvhenthe called subscribes/responds by removingfhis vreceiver from its switchliookithe current iiow over conductors 68 and 69is reversedenergizing relay ,621m series-withithe winding of impedance coil 70, upperg winding ofthe relay .and conductor 68.'

middle and lower windings ofrelay`61 tothe conductors 59 and 60 forzpurposes not related to this invention. `-VHowever,tl1e continuity springs and armatures of-relay, 62 complete this reversal without permitting the impulse -relayv61 to deenergizeso that-the slow releas-A ing relay Gifsy maintained energized to apply the holding ground tothe conductor 66. At

the closeoi this connection when theca-lling subscriber replaceshis receiver 4on thevswitclihook, the impulserelay 61 ,deenergizes' and shortly. theieater therein @it .riemergere Iii the event'that the repeater .has f 'connector switches.

the event that the 're-V vpeaterhas been connected to a short telephone line the drop inpotential across theA resistance In thel foregoing partof the description ,it

has been pointed out that a slow releasing .re-

lay80 is provided iin the first selector which is energized in multiple withthe holding ref lay 14 .of this selector over the conductorll leading to the succeeding switch such as afsef lector or connector. lay 8O Vis provided so that the line switch holds thefprimary'trunk lead-ing to the iirst selector for a predetermined interval after the remainderof the connectionhas beenreleased.

'This slow releasingrebeen disclosed in zo This arrangement is made so that if acalling l subcriber immediately desires to establish a second connection, commonlyknown as a recall,to a called linea'fterthe prior connection has been released, he may do so without the possible difficulty of iinding that-all primary trunks accessible to his line are in use. Y .It will be! obvious that'the'period of delay in releasveffen the calling subscriber a shorter or` longer well livi'iovvii retarding arrangement may be provided inconnection with-relay 8O to give the desired period ofdelay. l

What I @claim is zv A Y u l.` In al signalling system, impulse receiving means, acircuit including an impulse transmitter for transmitting impulses to said impulse receiving means, and means operating without inertia .to compensate for variations circuit..l i

f2. In a ksignalling system, impulse receiving meansfa circuitinclu'ding an impulse tranjsmitter ,flor transmitting impulses jto v said Y im.- 'pulse receiving means, and means including an velectron. discharge device to compensate for variations in intensity of signals at said impulse receiving means. v 3i Inga signalling system, llay provided with' an armature,

an impulse rea circuit incurrent and said impulse relay connected in be controlled atwillto i period in which/to `initiate a re-call. .Any

series in .'saidfcircuit whereby ak iiux is developedin saidrelay. andjmeans for developinga. supplemental iiuxin said relay in inverse .proportion to the strength of impulse inv ,said circuit hereby said relay attractsits armature uniformlyin spite et variationsin illteesitrie Seiiimrulssf I 110 in intensity of impulses transmitted over said ,Y

said I telephone lines 4. In a signalling system, an impulseirelay provided Vwith an armature,'-'al circuit 'including a source of 'current andan impulse transmitterv connected in vseries'wi'th said impulse relay wherebycurrent impulsesmay be transmitted to saidrelay todevelopa-fluxtherein, andineansiincluding an'electron dischargefdevice; for developing a`- supplemental `-fluir in 'said 'impulse'lrelay which isinversely proportional tothestrength Vofimpulses transmitted to 'saidjrelaywhereby'said impulse -relay attracts `its armature uniformlyl in *response to impulses of widely varying intensity.

5. In. a telephone systemfav plurality of telephonelines of varyingcharacteristics,l an impulse 'transmitter' for 'ea'chf Atelephoneiline, any impulse' receivingldevice, means 'for' Iconnecting said' impulsereceivingdevice and K a source'of current 'in series v'withY any'off said telephone lines vwhereby said impulse-receivingdevice is actuated in'varyingdegreesof intensity, and' means including Vafthermionic current of intensity inversely lproportional? to that of saidimpulses for causingjs'aid varying impulses to actuatesaidfimpu-lse receiving' de- "viceeuniformly f 6. In a telephone system;afplurality-bf telephone `lines L*of different 'characteristics, each telephone line ibei'ng kprovided with any impulse transmitt-erfimpulse re-V ceiving means including anv impulse-virelay rconne'ctible f to any of fsaid-'telephone lines,Y said impulse' relay having an 5Tarmature Yand a-windingf af sourceYI ofi current lcommonV to said telephone lines,'1nea 1isjfor connecting `said winding and said souree'o'f current in` series with any of said"4 ltelephone lines` whereby said "impulsevr'elay attracts Yfits armature with varying' degrees 'of intensity in response to impulses from theimpulse'transmitter ofthe connec'ztedftelephoneline, and means including anotlierlwinding onsaidimpulsejrelay and asource -of Fthermionic; current! variably controlled' bythe intensity Vof said impulses for causinglsaidfrelayi'to 'at'- tract'its` armature uniformly in" response' to impulses of varying characteristics. A

"--"72' Iii/anA automatic telephone system, telephone lines of various lengths each provided l with impulse 'transmitting means; an4 autofor directively adjusting saidf switchQ4 in` respon'sefto impulses front said impulse transmitting 'f means, and 'electrical-means' 'to' compensate "for variations? inf-the intensity f i impulses at'saidimpul'sereceiving mea-ns.

through said telephone line,"and^meansin when lca'llingf 5to Vsaid automatic switeh,"i'mpulse Irec'eivi'i-ig means `currentco1npensates for variationsY in imi pulse strength,` and*l other numerical switches directively'cont-rolled by said impulse relay. *9.'51112an= automatic telephone system, an

`impulserelay; an impulse vcircuit including animpulse transmitter and a windaba-ttery, ing tsaid impulse/relay whereby said impulse'transinitter may transmit impulses `to said'relay,` a 'source ofv anode current cooper- 'atingin 'the' control of said impulse relay, a'resistan'ce in'saidcircuiti' for developing a d'ropinpotential there-across' proportional tothefcurrentin said" circuit, and means governed'by lsaid* drop -in potential for Vvarying saidt'anodep current in inverse proportion to the "strength of said'eurrent.`

410Qg In a` telephone-system, an impulsecircuit including therein a battery,v a winding of afmulti-winding impulse relay, a resistance and an@ impulse "jtransmitterf connected in series; an Velectron`discharge devicehaving a cathode,J an anode-and a' control electrode, means `forenergizing said cathode,` a connection fromV said control'v electrode vtoY said 'cathode 'including an adjustable portion oi! said resistance, a. connection from said anode 'tosaidcathode including a second winding of 'said impulse relay and a source of anodegcur- Y nt; and switching-means controlled by said impulse relay. lfIn' atelephone system, an impulse circuit'including therein' abattery, al winding of a multi-winding impulse relay, aA resistance adanf'impulse' 'transmitter connected 'in'V series,'` anl electron discharge device having acathode,v` an anode and trede;A meansi' for Ienergizing said'cathode, a`

a control elecconnection fromsaid control electrode to'said "cathode :including an` adjustable `portion of 'saidf'resistancd a-connection from said Vanode to saidgcathode inclu-dinger secondfwinding of jsaidl rimpi'ilsel Y relay, a source of anode icurremt,"aiidnswitchingv means including primary-and Vsecondar'ymotorA` magnets successively controlled by said impulse relay.

1'2. In aitele'phone system, a. telephone line, switching Jmeans, means i for connecting said "switching'means to said-telepl1one line, said 'switching means including Ian impulse relay directively operated byimpulses transmitted lover'sa-id-'telephone line, af lsource of anodecurrent inversely qproportional in strength toj the lstrength ofimpulses ytransmitted' over :said telephone vline cooperating with sad'impulseA for uniformly operating said "impulse-relay 'to controlsaid switching means, a desiredi-"in'al connecting Vswitch selected by saidV switching means, meansresponsive Yto the-selection kof said final' selecting switchr f yfor 1 disconnecting said impulse relay `from further control' vfrom said ltelephone line, a second impulse relay associated with said final connecting switch arranged tobe directly controlled by impulses transf mitted over said telephone line, and means including a source of anode current inversely proportional vin strength to the impulses transmitted to said second impulse relay forv rendering the operation of said last named relay uniform under Varying conditions.

13. In an automatic telephone system, a plurality of telephone lines, a plurality of primary trunks, means for connecting an idle `primary trunk to a calling telephone line, means including other switches for extending the primary trunk connected to the calling telephone line with any wanted. telephone line, and means for retaining temporary connection from said last mentioned primary trunk to said calling telephone vline while releasing the remainder of the connection.

`lli) 14. In an automatic telephone system, VKa plurality of telephone lines each provided with a line switch, means including primary trunks, secondary trunks, primary and secondary numerical a telephone connection between any calling telephone line andl any wanted telephone line, and means for releasing said primary and secondary numerical' switches while temporarily retaining the connection between said calling telephone line and the primary trunk last used.

15. The method of handling a re-call in an automatic telephone system in which a normal connection between subscribers -is accomplished in successivestages which comprises always usi-ng the same primary stage that was used in a preceeding connection.

In witness whereof, I hereunto'subscribe my naine this 7th day of December, A.' D.

wmrimn rr. POWELL.`

vswitches for establishing v 

